Many microorganisms can utilize hydrocarbons as a primary carbon source, but potential hydrocarbon substrates are immiscible in water and are often intrinsically viscous. Before such hydrocarbons can be metabolized, they must first be converted to and maintained in a more accessable physical form. Numerous microorganisms accomplish this conversion by producing and exporting surface active and/or emulsifying agents that convert the insoluble, viscous, oil substrates into fine, stable oil-in-water emulsions. The result is a marked increase in the effective hydrocarbon surface area, through which far more effective assimilation and metabolism of the hydrocarbons may occur.
Among the microbes with this ability is Mycobacterium rhodochrous NCIB 9005, which Holdom et al. [J. Appl. Bacteriol. 32:448 (1969)] showed produces a nonionic surface active agent during growth on n-decane. Iguchi et al. [Agric. Biol. Chem. 33:1657 (1969)] found that Candida petrophilium produced a surface active agent consisting of peptides and fatty acid residues, while Suzuki et al. [Agric. Biol. Chem. 33:1619 (1969)] reported that trehalose lipid appeared in the oil phase of cultures of various Arthrobacter, Brevibacterium, Corynebacterium and Nocardia strains. Wagner has reported the production of trehalose lipids by Nocardia rhodochrous and Mycobacterium phlei and their use in oil recovery [U.S. Pat. Nos. 4,392,892 and 4,286,660].
Torulopsis gropengiesseri was found to produce a sophorose lipid, while rhamnolipids are reported by Hisatsuka et al. [Agric. Biol. Chem. 35:686 (1971)] to have been produced by Pseudomonas aeruginosa strain S7B1 and by Itoh et al. [Agric. Biol. Chem. 36:2233 (1971)] to have been produced by another P. aeruginosa strain, KY4025. The growth of Corynebacterium hydrocarboclastus on kerosene was reported by Zajic and his associates [Dev. Ind. Microbiol. 12:87 (1971); Biotechnol. Bioeng. 14:331 (1972); Chemosphere 1:51 (1972); Crit. Rev. Microbiol. 5:39 (1976); and U.S. Pat. No. 3,997,398] to produce an extracellular heteropolysaccharide which, among other properties, emulsified kerosene, Bunker C fuel oil and other fuel oils.
Gutnick et al. [U.S. Pat. Nos. 3,941,692; 4,230,801; 4,234,689 and 4,395,354] have shown that Acinetobacter calcoaceticus ATCC 31012 (RAG-1) produces at least two polyanionic protein-associated lipopolysaccharide biopolymers with strong activity as emulsion stabilizers. These interfacially active agents, collectively called emulsans, encapsulate the bacteria and are also released to the surrounding medium. More recently, Kaplan and Rosenberg [Appl. Environ. Microbiol. 44:1335 (1982)] showed that A. calcoaceticus BD-4 and BD-413 produce extracellular polymeric bioemulsifiers. The bioemulsifier from BD-413 contained rhamnose and glucose in a 3:1 molar ratio.
The ability to produce bioemulsifiers extends beyond the bacteria. For example, Cooper and Paddock [Appl. Environ. Microbiol. 47:173 (1984)] have reported that the yeast Torulopsis bombicola produces a mixture of glycolipids that act as a biosurfactant. Most of the surfactant is produced in the late exponential phase of growth when the yeast is cultured.